There are plenty of crazy guns out there. Some are only considered crazy because people simply weren't ready for their advanced design. Here are two of my favorites:
The Browning Recoilless shotgun:
Browning claimed that it reduced felt recoil by 70%. They were right. I owned one for a while and it really had a light recoil impulse, but was very barrel heavy. It never caught on.
The Ljutic Space Gun:
Al Ljutic was a rifle builder. A buddy invited him to go shoot Trap, but Al didn't have a shogtun; so he built one. The Ljutic Space Gun was born.
This gun was far ahead of its time. Al understood the value of having the recoil go straight into the shoulder rather than at an angle like most shotguns or rifles have. As you can see, the straight design brings the recoil straight into the shoulder. This helps reduce felt recoil and reduce muzzle rise which makes for easier follow through.
Instead of a traditional blade or stick trigger, it has a button. This is more comfortable to use. The pistol grip has the shooter keep their shooting hand more vertical which makes for more natural pointing. The bolt action made for a very simple mechanism which was super reliable.
Alas, the looks were something most shooters couldn't get past. The gun didn't sell well and was discontinued a long time ago. However, for the right money, Ljutic might still build you one today if you really wanted it.